Has anyone here ever had a use case for toLower() where they actually wanted localization to apply?

It seems to me that in practice, it's extremely rare to want to change case of real, natural-language text. When I have natural-language text, it's just a blob to me, and I don't want to touch it.

The only time I ever want to lower-case or capitalize something, I'm working with identifiers meant for computer -- not human -- consumption. Usually, specifically, I'm dealing with identifiers that have annoyingly been defined to be case-insensitive even though the only humans that ever see them are programmers and programmers hate case-insensitivity. HTTP headers are a common example.

I mostly write C++, and I end up writing code like:

    for (char& c: str) {
      if ('A' <= c && c <= 'Z') c = c - 'A' + 'a';
    }

Later on, some well-meaning developer on my team will come along and say "Ugh what is this NIH syndrome?" and then they "clean it up" as:

    #include <ctype.h>

    for (char& c: str) {
      c = tolower(c);
    }

And then I have to say NOOOOOOO DON'T DO THAT YOU HAVE NO IDEA WHAT tolower() REALLY DOES!

I struggle to imagine any real use case where you'd actually want locale-dependent tolower() other than, maybe, a word processor -- but if you're writing a word processor, you're probably not going to be depending on the language's built-in string APIs to do your text manipulation.